The traditional way to drill a well involves starting with a large bore and drilling ever decreasing bores below so that a new section of casing can fit through the casing already run and cemented. In this technique, as each segment is drilled there is what is called flat time or time when no drilling is going on. Instead, time, which costs the operator money, is taken up tripping the drill bit out of the hole and running in each size of casing.
One more recent alternative to this well used technique is a monobore completion. In this type of well drilling a single size hole is drilled from the surface to total depth. Even with this technique, unless the productive interval is relatively shallow, any time a problem zone is breached in the drilling, the drilling has to stop and the bit pulled out of the hole so that casing or liner can be run to isolate the problem zone so that drilling can resume. This technique is necessary because the mud weight is the sole means of well control during this type of drilling and the problem zone needs to be isolated with cemented casing or liner before drilling can resume safely.
Another known technique is to drill with a downhole motor powered by flow from coiled tubing going through a lubricator for well control. Although a bore can be continuously drilled this way, it is limited to rather small bore sizes.
Accordingly for the larger bores, even the monobore technique does not reduce the flat time from tripping in and out of the bore as each section of casing or liner is run in after a segment of the monobore is drilled.
What is needed is a technique that allows the ability to deal with problem zones of any type while drilling so as to isolate them without having to pull the bit out of the hole. This problem is addressed for applications where drilling with a downhole motor and coiled tubing through a lubricator will not produce the required bore diameter. The technique involves being able to isolate the zone with the drill string and bit still in the hole in a manner that allows drilling to resume as the zone is isolated. In part the solution involves the use of composite memory materials to be delivered with the drill string or subsequently over it when the troublesome zone is encountered. Local application of energy or heat activates the material to another shape to seal the troublesome zone and, if previously attached to the drill pipe, to release from it to allow drilling to resume. This general description will be more readily understood by those skilled in the art from a review of the description of the preferred embodiment and the claims, both of which appear below.